U.S. patent number 4,478,874 [Application Number 06/559,665] was granted by the patent office on 1984-10-23 for methods for improving the gas barrier properties of polymeric containers.
This patent grant is currently assigned to Cosden Technology, Inc.. Invention is credited to Granville J. Hahn.
United States Patent |
4,478,874 |
Hahn |
October 23, 1984 |
Methods for improving the gas barrier properties of polymeric
containers
Abstract
Methods are disclosed for the treatment of food, beverage, and
medicine containers and the like, which are made of organic
polymeric resins, to greatly increase the gas barrier properties
thereof. The containers are ion-plated with a very thin flexible
layer of an inorganic oxide.
Inventors: |
Hahn; Granville J. (Big Spring,
TX) |
Assignee: |
Cosden Technology, Inc.
(Dallas, TX)
|
Family
ID: |
24234513 |
Appl.
No.: |
06/559,665 |
Filed: |
December 9, 1983 |
Current U.S.
Class: |
427/525; 428/441;
428/430 |
Current CPC
Class: |
B05D
7/02 (20130101); B05D 7/24 (20130101); C23C
14/083 (20130101); C23C 14/32 (20130101); C23C
14/10 (20130101); Y10T 428/31616 (20150401); Y10T
428/31645 (20150401) |
Current International
Class: |
C23C
14/32 (20060101); B05D 7/24 (20060101); B05D
7/02 (20060101); C23C 14/10 (20060101); C23C
14/08 (20060101); B05D 003/14 (); C23C
011/08 () |
Field of
Search: |
;427/40,38,39
;428/430,451,441 ;204/192N |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Newsome; John H.
Attorney, Agent or Firm: Caddell; Michael J.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A method for decreasing the gas permeability of containers made
of polymeric resins, said method comprising:
placing clean empty polymeric containers in a vacuum chamber;
evacuating a substantial portion of the atmosphere from said
chamber;
vaporizing an inorganic oxide material in said chamber;
ionizing said vaporized material; and,
biasing said ionized material to impinge on a substantial portion
of the surface of said containers.
2. The method of claim 1 wherein said chamber is evacuated to a
level of around 1.times.10.sup.-5 Torr.
3. The method of claim 1 wherein said containers are made of a
thermoplastic polymer selected from the group consisting of
polyolefins and polyesters.
4. The method of claim 1 wherein said inorganic oxide material is
selected from the group consisting of silicon monoxide, titanium
oxide, tantalum oxide, and metallic oxides.
5. The method of claim 1 wherein said inorganic material is coated
uniformly on said containers to a thickness of up to about 500
Angstroms.
6. A method of improving the gas barrier characteristics of
containers made of organic resins, said method comprising coating a
substantial portion of the surface of said containers with an
inorganic oxide material by gasless ion plating.
7. A method of treating containers to reduce the ingress and egress
of gases through the walls thereof, said method comprising:
locating at least one of said containers in a vacuum chamber;
evacuating the atmosphere from said chamber to a vacuum of around
1.times.10.sup.-5 Torr;
locating in said chamber a plating material comprising an inorganic
oxide;
creating an ionized plasma of said inorganic oxide; and,
biasing said plasma toward said container and impinging it on said
container surface.
8. The method of claim 7 wherein said biasing step is continued
until a layer of up to 500 Angstroms thickness is created on said
container.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to plastic containers and
more particularly discloses containers, such as bottles and cans,
having improved gas transmission barrier characteristics.
In the food and beverage industry the trend is to move away from
packaging perishable products in glass and metal containers and to
substitute thermoplastic polymers for the container material. One
of the most successful polymers for beverage containers to package
beer, wine, and soft drinks has been polyethylene terephthalate
(PET). One of the largest markets for PET containers has been in
the two-liter carbonated drink field. Another area where PET is
expected to be used extensively is in packaging beer and food. In
either case, one of the most critical characteristics of the
polyester package is the prevention of gas permeation through the
wall of the container.
With carbonated soft drinks, the problem with gas permeation is the
loss of carbonation (CO.sub.2 gas) from the drink through the wall
of the bottle or can. Compared to the small, densely-packed metal
and glass molecules, polymer molecules are relatively large and
form a porous wall. Even the best polymer known at this time for
gas barrier properties, ethylene vinyl alcohol (EVOH), has poor
barrier ability when compared to the inorganics such as metals and
glass.
On the other hand, beer and food containers preferably should
present a good vapor barrier against the ingress of oxygen
(O.sub.2) into the container because of the accelerated spoilation
of the food products caused by the presence of oxygen therein.
While the use of PET two-liter containers has been relatively
successful, its use in smaller-sized containers such as half-liter
and one-third-liter, is very limited because of the greater
surface-area-to-volume ratios of the smaller containers, compared
to that of the two-liter container. This proportionate increase in
the surface area causes a much more rapid loss of carbonation from
and/or ingress of oxygen into the containers and thus decreases the
"shelf-life" of the contained product.
There have been several different methods developed in an attempt
to increase the "shelf-life" of plastic containers. One of the most
common methods involves creating a multi-layered container having a
thin barrier layer of a material such as EVOH or polyvinylidene
chloride (PVdC) buried between two or more layers of a container
polymer such as PET, polypropylene, polystyrene, or PVC. This
multi-layer container is difficult and expensive to manufacture
since the barrier layers are either expensive (EVOH) or corrosive
(PVdC). Also the process for forming a multi-layered material and
making a container from it may be much more complex than
single-layer processes.
Another method of creating a barriered polymer container is the
process known as "dip-coating". In this process a polymer bottle
made of a material such as PET, is first formed into its final
shape and then the additional step of dipping the container into a
coating solution is performed. This solution may be of a barrier
material such as PVdC. This process, in addition to adding another
expensive step to the container manufacture, also introduces a
material to the container that prevents easy recycling. Because of
the nature of PVdC, the coating must be removed by solvents before
the polymer container can undergo normal recycling. In light of the
trend toward compulsive container return laws in various states and
a probable federal deposit/return law, all future container designs
must be quickly and easily recyclable. Dip-coated bottles do not
lend themselves to easy recycling.
The present invention overcomes the deficiencies of the
barrier-layer containers and the dip-coated containers by providing
a barrier-treated plastic container which provides excellent
barrier characteristics, is cheaply and easily treated, and can be
completely recycled by conventional recycling techniques without
need for removal of dip-coated layers.
This is achieved by impregnating the surface of a normal polymer
container with an inorganic material such as a metallic oxide. The
impregation is done by gasless ion plating to provide an ultra-thin
flexible coating of the inorganic material on the plastic
substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the process of the present
invention.
FIG. 2 is a magnified cross-sectional schematic view of a coated
polymer material.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In one embodiment of the present invention, a number of one-half
liter polyester bottles (polyethylene terephthalate) were placed in
a vacuum chamber and a vacuum of about 1.times.10.sup.-5 Torr was
drawn on the chamber. A plating source comprising silicon monoxide
(SiO) was vaporized into a metallic oxide vapor. The vapor was
ionized into a plasma by an RF energy source and then biased by a
DC bias to impinge the substrate (bottle) surface with a
sufficiently high energy level to penetrate the SiO ions partially
into the substrate polymer. This process is generally the same as
that disclosed for metallic and non-metallic substrates in U.S.
Pat. Nos. 4,016,389, 4,039,416, Re 30,401, and 4,342,631, which
patents are hereby incorporated by reference into this
application.
Referring now to FIG. 1, which is a schematic illustration not
drawn to scale, disclosed is a vacuum chamber 10 having a substrate
holder 11 removably secured therein. At least one plastic bottle 12
is loosely held on the portable fixture 11 below a source of
inorganic material 15 held in a vaporizing filament 13. Filament 13
is electrically connected to and supported by a pair of terminals
14. It preferably is a resistance heating element powered by an
external AC power supply (not shown). As the coating material 15
held in filament 13 is vaporized by the filament, an ionizing
energy, comprising RF (radio frequency), and a biasing DC voltage ,
are placed on the filament 13 with respect to the substrate holder
11 which is grounded.
As a result of the vaporization of the source material and the
ionizing and biasing field created by the DC/RF power supply, a
plasma of ionized SiO particles forms between the filament 13 and
the substrate holder 11. The bias also accelerates the SiO ions
toward the fixture 11a which is located inside the bottle 12. The
ions impinge the outer surface of the polyester bottle while
traveling at very high velocities and apparently even penetrate
partially into the surface of the polymer. An even coating can be
obtained by rotating the bottle 12 about one or more of its axes
during the impingement cycle.
The impingement cycle is maintained long enough to obtain a coating
layer of around 500 angstroms thickness. The result is a clear
flexible coating of SiO on the outer surface of the polyester
bottle, which it is believed actually penetrates partially into the
polymer and plugs the interstices and porosities between the
polymer chains. This plugging of the interstices is believed to be
a main contributor to the improvement in gas barrier
characteristics of the SiO coated container. While 500 Angstroms is
considered a good coating thicknes, other thicknesses ranging from
less than 500 to as high as 5000 Angstroms or more might be used
depending on the type of polymer used, the container shape, and the
size and thickness of the container.
For example, a series of PET half-liter bottles were ion-plated
with SiO, and the measured CO.sub.2 transmission rate was reduced
from 4.0 to 1.7 ##EQU1## A pressure test was performed over a
period of time to determine if flexure during filling or stretching
under pressure by the container caused degradation or flaking off
of the inorganic material. It was observed that flexure and creep
did not significantly degrade the barrier characteristics. Manual
flexure of several containers was also performed to test for
cracking or flaking of the coating. After these steps were
performed, acetone was applied to the coated surface to detect any
breaks in the integrity of the coating. Since acetone will not
attack inorganics like SiO.sub.2 but is a strong solvent for the
polymer, any break in the SiO coating would have allowed the
acetone to attack the container polymer. No dissolving of the
container was observed after application of the acetone to the
outer surface. Thus flexure and creep not only had no effect on the
barrier properties they also had no detrimental effect on the
surface continuity of the coating.
In addition to the impingement coating of polyesters such as PET it
is believed that most other polymers can also be coated
successfully. It is also expected that other inorganic materials
may be substituted for SiO, for example aluminum oxide and titanium
oxide. Most inorganic or metallic oxides should be adaptable to
this process. It should also be noted that even though the metals
of these plating compounds are generally opaque, their oxides are
clear and thus they can be used on both clear and pigmented
polymers without affecting the aesthetics of the containers.
Recyclability of the used coated containers is not affected
detrimentally because of the extremely small amount of inorganic
coating used. Because of its inert nature and presence in small
amounts, the coating will not be noticeable in the recycled
polymer. The amount of inorganic coating is less than 1% by weight
of the polymer in the container. Some containers have inorganic
pigments such as titanium dioxide mixed with their polymers in
amounts as high as 25% by weight without affecting recyclability;
therefore it can be seen how negligible the effect of the coating
material is on recyclability using the present invention.
Referring now to FIG. 2, there is illustrated a schematic enlarged
illustration of a section of the coated surface indicating how it
is believed that the present invention increases barrier
properties. In the drawing, which is not an attempt to show true
scale, polymer molecules P are shown having long, winding structure
which when combined together result in large openings therebetween.
Inorganic metalic oxide molecules M, such as Silicon Oxide or
Aluminum Oxide, are very small and compact and can be infiltrated
into the interstices formed by the long bulky polymer molecules.
Because of the vacuum environment around the substrate and the high
velocity of impingement during the plating, the inorganic molecules
can penetrate deeply into the polymer interstices, giving good
binding between the coating and the substrate. A very thin layer,
on the order of around 500 Angstroms, of the metallic oxide is
applied to the substrate, giving a good barrier in the interstices
and having sufficient flexibility to withstand breakage when
flexed.
Although a specific preferred embodiment of the present invention
has been described in the detailed description above, the
description is not intended to limit the invention to the
particular forms or embodiments disclosed therein since they are to
be recognized as illustrative rather than restrictive and it will
be obvious to those skilled in the art that the invention is not so
limited. For example it is contemplated that plating materials
other than silicon monoxide, aluminum oxide, and titanium oxide can
be used. One such material would be tantalum oxide. Also containers
other than carbonated beverage bottles would benefit from the
present invention, such as beer containers, food containers, and
medicine containers. Thus the invention is declared to cover all
changes and modifications of the specific examples of the invention
herein disclosed for purposes of illustration, which do not
constitute departures from the spirit and scope of the
invention.
* * * * *